The present invention relates to a method for producing an organic thin film device and a transfer material usable for the method, particularly to a method of providing an organic thin film of an organic EL device (organic electroluminescent device).
Recently, much attention has been paid to organic light-emitting devices such as organic EL devices that can be easily applied to a surface light-emitting device. Specifically, the organic light-emitting device has been considered to be useful as an economical, solid emission type, light-emitting device having a large emission area such as a full color display device and a writing light source array, thereby having been actively studied. The organic light-emitting device generally comprises a couple of electrodes, a transparent electrode and a back side electrode, and a light-emitting organic thin film disposed between the electrodes. When to the organic light-emitting device is applied an electric field, electrons are injected from the back side electrode and holes are injected from the transparent electrode to the light-emitting organic thin film. The electrons and the holes are re-combined in the light-emitting organic thin film and energy is converted into light while an energy level is turned from a conduction band to a valence band, whereby the organic light-emitting device emits light.
The organic thin film in the organic light-emitting device has been generally provided by a vapor deposition process. Patterning methods for the organic thin film have been proposed in view of development of color image emission. For example, U.S. Pat. No. 5,294,869 disclosed a patterning method using a shadow mask. However, this patterning method needs a complicated vapor deposition apparatus to be poor in productivity and positional accuracy of patterning.
To overcome the above problems in patterning, Japanese Patent Laid-Open No. 9-167684 disclosed a method where an organic thin film is uniformly provided on a mica temporary substrate by a vapor deposition process beforehand, and the organic thin film is disposed closer to a substrate and selectively vapor-deposited onto the substrate in a pattern. Further, Japanese Patent Laid-Open No. 2000-195665 disclosed a method where an organic thin film is uniformly provided on a film temporary substrate by a vapor deposition process beforehand, and the organic thin film is disposed closer to a substrate through a mask and vapor-deposited onto the substrate in a pattern of the mask. These methods using the vapor deposition source provided on the temporary substrate are disadvantageous in that the vapor deposition process is poor in productivity and that only a low molecular weight organic compound can be used for the organic thin film.
Polymer-type organic light-emitting devices using a light-emitting organic thin film made of a polymer or a low molecular weight organic compound dispersed in a binder resin also have been known. Examples of the polymer include poly(p-phenylenevinylene) for green light emission (Nature, Vol. 347, Page 539, 1990), poly(3-alkylthiophene) for red-orange light emission (Japanese Journal of Applied Physics, Vol. 30, Page L1938, 1991), polyalkylfluorene blue light emission (Japanese Journal of Applied Physics, Vol. 30, Page L1941, 1991), etc. Such polymer-type organic light-emitting devices can be easily increased in emitting area to be useful for a flexible device. However, the light-emitting organic thin film cannot be provided by a vapor deposition process, whereby the light-emitting organic thin film is generally provided by a wet method.
As a method for providing a patterned, light-emitting organic thin film of the polymer-type organic light-emitting device, an ink-jet method, a printing method, etc. have been proposed. However, the patterned, light-emitting organic thin film provided by such a method is insufficient in uniformity of thickness because of a surface tension of a solution used in the method. Further, in the case of providing a laminate of a plurality of organic thin films, components is dissolved and mixed around a boundary of each film. Thus, the polymer-type organic light-emitting device utilizing the patterning method is poor in light-emitting efficiency and durability.
Expectations are high for a plastic film of a high molecular weight material as a flexible substrate of the organic light-emitting device. However, the plastic film is poor in oxygen- and water-resistance to be far from practicable, so that the substrate is generally made of a glass. The glass substrate is more difficult in handling than the plastic film, thereby reducing productivity in wet method. Further, in the case of using the plastic film substrate, the transparent electrode and a thin film transistor are laminated on the substrate to be costly. Coating such a substrate with the organic thin film is disadvantageous in yield and economical efficiency. Thus, there has been increasing need for a patterning method usable for production of the polymer-type organic light-emitting device.
WO 00/41893 disclosed a method using a donor sheet comprising an organic thin film and a photo-thermal conversion layer, where the organic thin film is thermally transferred to the substrate in a desired pattern by a laser. Such a thermal transfer method is disadvantageous in that a gas often penetrates into an interface between the organic thin film and the substrate. In the organic light-emitting device produced by this method, light-emitting efficiency, durability and uniformity of a light-emitting surface depend on conditions of the interface, and light-emitting properties are worsened by the penetration of a gas.
Further, in thermal writing-patterning method using a thermal head or a laser that is utilized in printing technique, temperature distribution expands around the pattern due to thermal diffusivity so that outlines of the organic thin film cannot be formed accurately. Thus, organic light-emitting devices produced by this method vary in amount of emission and has a defect due to an electric inferiority or a break of the organic thin film to be poor in durability. Further, there is a case where yield is lowered by poor positional accuracy of the substrate and the thermal head or the laser.
An object of the present invention is to provide a method where an organic thin film is uniformly provided by a wet method, etc., so that an organic thin film device such as an organic EL device excellent in light-emitting efficiency, uniformity of light emission and durability is efficiently produced with a simple apparatus and reduced cost. Another object of the present invention is to provide a transfer material usable in the method.
As a result of intense research in view of the above objects, the inventors have found that an organic thin film device such as an organic EL device excellent in light-emitting efficiency, uniformity of light emission and durability can be produced with excellent efficiency and reduced cost by a method where an organic thin film is provided on a temporary substrate by a wet method, etc. and transferred to a substrate. The present invention has been accomplished by the finding.
Thus, the first method for producing an organic thin film device according to the present invention comprises the steps of: making an organic thin film of a transfer material face a substrate, the transfer material having the organic thin film on a temporally substrate; decompressing a space between the transfer material and the substrate to bring the transfer material in contact to the substrate; heating at least one organic thin film; and peeling the temporary substrate from the organic thin film to transfer the organic thin film to the substrate.
In the first method, the organic thin film may be transferred to the substrate in a minute pattern by the steps of: placing a mask having a plurality of openings in the minute pattern between the transfer material and the substrate; decompressing spaces in the openings between the transfer material and the substrate to bring the transfer material in contact to the substrate; heating at least one organic thin film; and peeling the temporary substrate from the organic thin film. Each of the openings of the mask is preferably tapered from the transfer material side to the substrate side. It is preferred that the mask has an aperture connected with the openings and the spaces are decompressed through the aperture. Further, the aperture preferably comprises recesses provided on the bottom of the mask. The mask is preferably made of a material selected from the group consisting of metals, glasses, ceramics and heat resistant resins.
The second method according to the present invention is for producing an organic thin film device where a laminate of a plurality of continuous or patterned organic thin films is provided on a substrate by repeating a peeling-transfer process. The peeling-transfer process comprises the steps of: making an organic thin film of a transfer material face the substrate, the transfer material having the organic thin film on a temporally substrate; bringing the transfer material in contact to the substrate; heating at least one organic thin film; and peeling the temporary substrate from the organic thin film to transfer the organic thin film to the substrate. In the second method, it is preferred that the transfer material is brought in contact to the substrate while decompressing a space between the transfer material and the substrate.
In the first and second methods according to the present invention, each of a blue light-emitting organic thin film, a green light-emitting organic thin film and a red light-emitting organic thin film may be transferred to the substrate in a minute pattern to provide a light-emitting organic thin film comprising pixels of blue, green and red arranged repeatedly. The organic thin film is preferably heated at 40 to 200xc2x0 C. Further, it is preferred that the organic thin film is provided on the temporally substrate by a wet method.
The third method for producing an organic thin film device according to the present invention comprises the steps of: making a light-emitting organic thin film comprising patterned pixels of blue, green and red of a transfer material face a substrate, the transfer material having the light-emitting organic thin film on a temporally substrate; bringing the transfer material in contact to the substrate; heating at least one light-emitting organic thin film; and peeling the temporary substrate from the light-emitting organic thin film to transfer the light-emitting organic thin film to the substrate. In the third method, it is preferred that the transfer material is brought in contact to the substrate while decompressing a space between the transfer material and the substrate. The light-emitting organic thin film is preferably heated at 40 to 200xc2x0 C. Further, it is preferred that the light-emitting organic thin film is provided on the temporally substrate by a wet method.
A transfer material of the present invention comprises a temporary substrate and a light-emitting organic thin film provided on the temporary substrate by a wet method, etc., the light-emitting organic thin film comprising patterned pixels of blue, green and red. The transfer material of the present invention can be used in the third method.
The organic thin film device produced by the first, second or third method preferably comprises a light-emitting organic thin film or a carrier-transporting organic thin film, more preferably comprises a hole-transporting organic thin film, a light emitting organic thin film and an electron-transporting organic thin film disposed in this order from the substrate side. Further, the light-emitting organic thin film preferably comprises pixels of blue, green and red arranged repeatedly. The substrate preferably comprises a support and a transparent electrically conductive layer disposed on the support.